Innovative Methodology Mapping and quantifying hyperpolarized He magnetic resonance imaging apparent diffusion coefficient gradients

Evans A, McCormack DG, Santyr G, Parraga G. Mapping and quantifying hyperpolarized He magnetic resonance imaging apparent diffusion coefficient gradients. J Appl Physiol 105: 693–699, 2008. First published June 5, 2008; doi:10.1152/japplphysiol.00178.2008.—We measured hyperpolarized He magnetic resonance imaging (MRI) apparent diffusion coefficients (ADC) and quantified ADC gradients in each threeby-three voxel region of interest (ROI). Such local ADC gradients can be represented in vector maps showing the magnitude ( G3 3 ) and direction of ADC gradients, providing a qualitative visualization tool and quantitative measurement of airway and air space heterogeneity. Twenty-four subjects (15 male, mean age 67 7 yr) with global initiative for chronic obstructive lung disease (GOLD) stage II (n 9, mean age 68 6 yr), GOLD stage III chronic obstructive pulmonary disease (COPD; n 7, mean age 67 8 yr), and age-matched healthy volunteers (n 8, mean age 67 6 yr) were enrolled based on their age and spirometry results. Hyperpolarized He MRI was performed on a whole body 3.0 Tesla system. Mean He ADC and ADC standard deviation were calculated for the center coronal slice, and the mean magnitude and direction of the ADC gradient vectors were calculated for each three-by-three voxel matrix ( G3 3 ). While the He ADC standard deviation was not significantly different, mean G3 3 was significantly different between subjects with stage II (0.14 0.03 cm/s) and stage III COPD (0.19 0.03 cm/s; P 0.005) and between healthy subjects (0.12 0.03 cm/s) and those with stage II COPD (P 0.02). The second order statistic G3 3 may provide a sensitive measure of ADC heterogeneity for ROI representing 9.4 9.4 30 mm or 2.6 cm of lung tissue.